1. Field of the Invention
The invention relates generally to carbon nanotubes enclosing a foreign material.
2. Description of Related Art
Fullerenes are a family of closed caged molecules formed entirely of carbon in the sp2-hybridized state and constitute the third form of carbon after diamond and graphite. These spherical, cavity containing molecules and their allotropes have been found to possess novel, remarkable properties, and the buckminster fullerene C60 has been widely investigated.
In 1991 Sumio Iijima synthesized new carbon structures in the form of needlelike tubes with multiple concentric cylindrical shells of hexagonally bonded carbon atoms. These extended fullerene tube structures have been called carbon nanotubes, more specifically multiwalled nanotubes (MWNTs). These MWNTs have typical outside diameters from a few to several tens of nanometers.
It has been reported that foreign materials, other than carbon have been encapsulated or introduced into MWNTs, such as metals, semiconductors, superconductors, magnetic materials, alkali metals, gases, and organic molecules. Ajayan, P. M., et al., have reported that only a very small fraction of the MWNTs (about 1%) enclosed foreign materials [Nature, Vol. 361:333–334 (1993)]. In a companion paper, they reported the introduction of bismuth oxide into MWNTs [Ajayan, P. M., et al., Nature, Vol. 362:522–525 (1993)]. U.S. Pat. No. 5,547,748 discloses a multi-walled carbon nanotube of between 5 nm and 1000 nm encapsulating metals from the actinide or lanthanide series, paramagnetic or ferromagnetic elements, and metal alloys. Dujardin et al have described wetting and filling MWNTs with substances having low surface tension, such as sulfur, selenium, and cesium, with an upper limit to this tension of less than 200 millinewtons per meter [Dujardin, E., et al., “Capillarity and Wetting of Carbon Nanotubes, Science”, Vol. 265:1850–1852 (1994)]. Compounds of yttrium [Seraphin. S., et al., Nature, Vol. 362:503 (1993)], manganese [Ajayan, P. M., et al., Phys. Rev. Lett., Vol. 72:1722–1725 (1994)], and gadolinium [Subramoney, S., et al., Carbon, Vol. 32:507–513 (1994)] were encapsulated in MWNTs. It has been reported that oxides of nickel, cobalt, iron, and uranium can be encapsulated by opening MWNTs and depositing the filling material by wet chemical techniques [Tsang, S. C., et al., Nature, Vol. 372:159–162 (1994)]. MWNTs have been filled with silver, gold, and gold chloride [Chu, A., et al., Chem. Mater, Vol. 8:2751–2754 (1996)]. MWNTs were filled with Cr, Ni, Dy, Yb, and Gd, and particles of Pd, Fe, Co and Ni have been encapsulated within nanotubes [Guerret-Piecourt, C., et al., “Relation between metal electronic structure and morphology of metal compounds inside carbon nanotubes”, Nature, Vol. 372:761–765 (1994)]. MWNTs can be created with acidic functionality, with basic or hydrophobic functionality, or with biomolecular probes at the open tip ends of the MWNTs [Wong, S. S., et al., “Covalently functionalized nanotubes as nanometer-sized probes in chemistry and biology,” Nature, Vol. 394:52–55 (1998)]. Proteins and enzymes can be immobilized on the inner surfaces of MWNTs [Davis, J. J., et al., Inorganica Chimica Acta, Vol. 272:261–266 (1998)].
In 1993 it was discovered that the use of transition metal catalysts during arc discharge produced single walled nanotubes (SWNTS) [Bethune, D. S., et al., Nature, Vol. 363:605–607 (1993), Iijima, S., et al., Nature, Vol. 363: 603–605 (1993)]. Kiang, C -H et al described the synthesis of SWNTs with a metal catalyst [Kiang, C. -H., et al., J. Phys. Chem. Solids, Vol. 57:35–39 (1995); Kiang, C. -H., et al., J. Phys. Chem., Vol. 98: 6612–6618 (1994); Kiang, C. -H., et al., Carbon, Vol. 33: 903–914 (1995); Kiang, C. -H., et al., Chem. Phys. Lett., Vol. 259:41–47 (1996)].
SWNTs are generated by arc-evaporation, by laser-vaporization of metal-doped graphite, by thinning of MWNTs using CO2 by pyrolysis of the hydrocarbon, and by chemical vapor deposition. It has been reported that hydrogen gas can condense inside SWNTs [Dillon, A. C., et al., “Storage of hydrogen in single-walled carbon nanotubes”, Nature, Vol. 386:377–379 (1997)]. It has also been reported that elongated crystallites of Ru were encapsulated in SWNTs [Sloan, J., et al., The opening and filling of single walled carbon nanotubes (SWTs), Chem. Commun., Vol. 3: 347–348 (1998)]. SWNTs exhibit both a smaller range of diameter and far fewer defects than MWNTs [Service, R. F., “Superstrong Nanotubes Show They Are Smart, Too”, Science, Vol. 281:940–942 (1998); Sloan, J., et al., supra].
Nanotubes are superstrong and light, and can act as both conductor or semiconductor depending on the diameter and chirality of the hexagonal carbon lattice along the length of the nanotube [Dekker, C., “Carbon Nanotubes as Molecular Quantum Wires”, Physics Today, Vol. 52: 22–28 (1999), Ebbeson, T. W., “Carbon Nanotubes”, Physics Today, Vol. 49:26–32 (June 1996)]. Molecular electronics and nanoscale molecular surgery are but a few of the applications requiring strong, stable, small diameter nanotubes that enclose foreign materials that are capable of forming a thread-like structure having a solid form at ambient temperatures and pressures and that have few defects.